Forum Discussion
Honored ContributorCreating a bidirectional bus
I want to connect a USB chip (FT245R) to a CPLD. To do that I need a bidirectional 8-bit bus. I thought I could declare the pins to be bidirectional and with a mux, read to or write from the pins as necessary. My Verilog code for the mux is:
[code]
always @(negedge clk) begin: TESTUSB_MUX
if ((TXE == 0)) begin
USBBUS <= OUTBUS;
end
else if ((RXF == 0)) begin
INBUS <= USBBUS;
end
end
[\code]
But the Fitter generates errors, e.g., Error: Can't reserve pin "USBBUS[0]" because its name already exists with a different direction
How can a bidirectional bus be created?
13 Replies
Altera_Foruminout port bidir can be either a wire set by an assign statement or a reg set in the sequential code, but not both at a time.
I'm under the impression that you are overcomplicating a basically simple thing.- Altera_Forum
No doubt, but how about suggesting how I could simplify things and come up with something that works?
- Altera_Forum
Your code from post# 2 can basically work, if USBBUS is declared as inout and all variables assigned in the always block as reg.
Functional detail related to your application are a different thing, but you get legal Verilog syntax as a starting point.
